In recent years, portable electronic devices such as mobile phones and notebook-sized personal computers have become increasingly popular. These portable electronic devices widely use nonaqueous electrolyte cells such as a lithium-ion battery. In addition, also in the automobile industry, the nonaqueous electrolyte cells are attracting attention as power sources for electrically-powered cars and hybrid vehicles both of which cope with environmental problems.
Most nonaqueous electrolyte cells include an element unit in which a pair of electrodes are disposed to face each other with a separator therebetween; an electrolytic solution; and a container for accommodating them. In general, this container includes a metal case having an opening, and a sealing body for sealing the opening. Moreover, in order to ensure electrical insulation between the metal case and the sealing body, a gasket is sometimes interposed between them.
In a nonaqueous electrolyte cell, it is important to prevent infiltration of moisture into the element since moisture has an adverse effect on the electrolytic solution (in particular, on the electrolyte) and the electrodes. In addition, it is required to prevent the electrolytic solution from leaking out or evaporating. Accordingly, a sealant is provided between the metal case and the sealing body, or between the gasket and the metal case or the sealing body.
Further, the sealant may contain a pigment, a dye and the like in order to improve visibility. For example, Patent Literature 1 discloses a sealant containing an inorganic pigment, and Patent Literature 2 discloses a sealant containing phthalocyanine blue which is an organic pigment.